Smith wrote that a connection between worsening storms and climate change has been “widely debunked,” and that the United Nations doesn’t believe that warming is related to “more severe weather disasters.” Both claims are incorrect. There is some evidence linking climate change to worsening hurricanes, droughts and other disasters.

He mentioned an oft-repeated claim that there has been a “lack of global warming over the past 15 years.” Though the rate of warming has slowed, the world does indeed continue to warm, and cherry-picked data underlie the claims that warming has stopped. See update below.

Smith quoted an InterAcademy Council report as saying the U.N.’s climate reports had “significant shortcomings in each major step” of the U.N.’s assessment process. That’s misleading. The report found that though there is certainly room for improvement, the U.N.’s process has been “successful overall.”

Smith, April 23: The White House’s Climate Assessment implies that extreme weather is getting worse due to human-caused climate change. The president regularly makes this unsubstantiated claim – most recently in his Earth Day proclamation, citing “more severe weather disasters.”

The relationship between increasing severe weather events and climate change is more complicated than Smith reports. We asked Smith’s office for clarification, and a spokesman, Zachary Kurz, sent us a number of links to and quotes from various documents from the Intergovernmental Panel on Climate Change, the United Nations body that releases periodic reports on the entirety of climate change science. The citations Kurz sent were generally cherry-picked lines from very long and complicated reports. His list ignored other lines from the same reports, as well as evidence published elsewhere.

There is, in fact, some evidence that climate change is linked to more severe hurricanes, droughts and other weather disasters.

First, the “worsening-storms scenario” has not in fact been debunked. Kurz pointed us to the IPCC’s 5th Assessment Report and noted that hurricane frequency and intensity has shown no trend over time. This is misleading.

The IPCC did find that there is “low confidence” regarding “increases in tropical cyclone activity” over the past 100 years, but evidence is stronger regarding increases in the strongest storms in certain regions. According to the same chapter of the IPCC report, there is evidence for a “virtually certain” — which means between 99 percent and 100 percent probability — “increase in the frequency and intensity of the strongest tropical cyclones since the 1970s” in the North Atlantic basin.

This is an important point in climate science: The changes due to warming are and will continue to be varied across different parts of the world. For example, as the National Oceanic and Atmospheric Administration has described, the Arctic is warming at twice the rate of other parts of the world. Just because the global trend in tropical cyclones is generally flat, that does not mean that there can’t be “worsening storms” in certain specific areas.

Smith is correct that the White House’s Climate Assessment “implies that extreme weather is getting worse due to human-caused climate change.” As the assessment notes, “There has been a substantial increase in most measures of Atlantic hurricane activity since the early 1980s, the period during which high-quality satellite data are available. … These include measures of intensity, frequency, and duration as well as the number of strongest (Category 4 and 5) storms.”

Smith went too far when he called the White House assessment of human-caused extreme weather “unsubstantiated.” It’s true that some studies have found that natural variability in the climate system may be responsible, but others have indeed found that anthropogenic — human-caused — warming is at root. This view was endorsed in a 2014 summary published jointly by the U.S. National Academy of Sciences and its British equivalent, the Royal Society:

NAS & Royal Society, February 2014: Earth’s lower atmosphere is becoming warmer and moister as a result of human-emitted greenhouse gases. This gives the potential for more energy for storms and certain severe weather events. Consistent with theoretical expectations, heavy rainfall and snowfall events (which increase the risk of flooding) and heatwaves are generally becoming more frequent. Trends in extreme rainfall vary from region to region: the most pronounced changes are evident in North America and parts of Europe, especially in winter.

That report agrees that the science on hurricanes in general is not settled, but that hurricanes are likely to become larger and more powerful as the world warms.

Looking ahead, evidence supports the president’s concern about increasing storm severity. According to NOAA, human-caused global warming likely will make hurricanes more intense by between 2 percent and 11 percent by the end of this century; there are also “better than even odds” that there will be an increase in “the numbers of very intense hurricanes in some basins.” A study published in the journal Science in 2010 projects “nearly a doubling” of category 4 and 5 hurricanes by 2100, though an overall decrease in the frequency of all tropical cyclones.

For other types of extreme weather events, there is also some degree of support for the idea that climate change is making things worse. For example, the IPCC report says that “there is medium confidence that some regions of the world have experienced more intense and longer droughts” — this is true in areas like Europe and West Africa, though not true in parts of North America and Australia. A 2013 Nature Climate Change paper, written by experts with the Institute for Atmospheric and Climate Science in Zurich, found that “severe and widespread droughts” are likely over the next 30 years to 90 years in many parts of the world.

According to the IPCC, there is also “medium confidence” that human influence has caused increases in extreme precipitation events, and “[t]here are likely [66 percent to 100 percent] more land regions where the number of heavy precipitation events has increased than where it has decreased.” A study published on April 27 in Nature Climate Change attributed 18 percent of current “moderate precipitation extremes” and 75 percent of “moderate hot extremes” to human-caused warming, and warned that the contribution to these severe events will increase dramatically as the world continues to warm.

Extreme Events or Economic Losses?

Smith also mischaracterized a United Nations report. In his op-ed, he wrote that “[e]ven the UN doesn’t agree” with this statement from Obama’s Earth Day proclamation: “The costs of more severe weather disasters can be measured in lost lives and livelihoods and in billions of dollars of emergency services, and the costs will only increase with time.”

Smith cited the IPCC’s 2012 Special Report on Extreme Events, claiming that it found “high agreement” that “long-term trends in weather disasters are not attributable to human-caused climate change.” But that’s not the case.

Kurz told us that Smith was actually basing this claim on a statement in the IPCC report regarding not weather disasters themselves but rather “long-term trends in normalized losses” resulting from those disasters. There’s a big difference. The report actually does say that human-caused warming has led to changes in some examples of extreme weather. The IPCC says, “There is evidence that some extremes have changed as a result of anthropogenic influences.”

The IPCC’s extreme events report did note that studies are split on whether one can attribute increasing monetary losses from weather disasters to climate change, or solely to socioeconomic changes. (A hurricane that hit a major city in 2015 will cause far greater economic losses than one that hit in 1915 — there are more buildings to fall down, more people to be injured and so on.) That does not mean that “even the UN doesn’t agree” with Obama’s proclamation, as Smith claimed. In fact, the IPCC’s report concludes on this issue: “[M]any studies underline that both factors need to be taken into account, as the factors do in fact amplify each other, and therefore need to be studied jointly when expected losses from climate change are concerned.”

The 15-Year Pause, Redux

Smith also wrote that “[c]limate alarmists have failed to explain the lack of global warming over the past 15 years.” This is misleading for two reasons: Though the rate of warming has slowed, there has indeed been warming in that period, and climate “alarmists” – scientists, actually – have indeed managed to explain that slowdown.

As we have written before, claims regarding a lack of warming over the past 15 to 17 years often rely on the use of 1998 as a starting point. That year was particularly warm, and thus comparing it with more recent years will yield little or no warming. Choosing another year surrounding 1998, however, would show significant warming – both methods are examples of cherry-picking, though, and the long-term trends tell us more about what is happening to the climate.

Kurz quoted the IPCC’s 5th Assessment report, which refers to “the recent hiatus in global mean surface temperature rise.” But as that report explains in detail, the “hiatus” does not mean warming has stopped. For example, it acknowledges that the rate of warming from 1998 to 2012 — 0.05 degrees Celsius per decade — was smaller than the trend since 1951 (0.12 degrees C per decade). However, “[t]rends for short periods are uncertain and very sensitive to the start and end years. For example, trends for 15-year periods starting in 1995, 1996, and 1997″ are 0.13, 0.14 and 0.07 degrees C per decade. In other words, one can make the hiatus nearly disappear, in relation to the longer-term trend, just by shifting by one or two years.

Furthermore, even though there has been a slowdown in warming — not a pause in total, but a decrease in the rate at which the Earth is warming up — scientists have offered explanations for it. For example, a paper published in Sciencein February of this year found that the slowdown was caused by ocean cycles in the Atlantic and Pacific (known as the multidecadal oscillations) — and that this trend “will likely reverse” and add significantly to warming in the coming decades.

Though again, single data points in either direction are less important than the trend, 2014 was likely the warmest year since record-keeping began, and January to March of this year was likely the warmest such period on record as well.

Update, June 5: Though the IPCC concluded in 2012 that a “hiatus” in warming occurred from around 1998 through recent years, a new report published in the journal Science by National Oceanographic and Atmospheric Administration scientists has called that conclusion “no longer valid.”

The researchers updated temperature data sets to better reflect the readings taken from ships and floating buoys, as well as from land-based temperature stations. They found that the warming trend from 2000 to 2014 was 0.116 degrees C per decade – a number that is “virtually indistinguishable” from the earlier and longer period from 1950 through 1999 (0.113 degrees C per decade). Even if they shifted the more recent trend to 1998 through 2014, which features a very warm starting year, the trend was similar — 0.106 degrees C per decade.

In other words, as the study’s lead author told the Associated Press, “the reality is that there is no hiatus.” The world has continued to warm in recent years, at about the same rate as in decades prior.

Spinning a Critique of the IPCC

Smith also engaged in a bit of spin in his op-ed in his citation of the InterAcademy Council. This is a group made up of major science academies from around the globe — including the U.S. National Academy of Sciences — that provides advice to international bodies such as the United Nations. Smith mentioned the council’s review of the IPCC’s 2008 Fourth Assessment Report:

Smith, April 23: The InterAcademy Council, a multinational scientific organization, reviewed the report in 2010 and identified “significant shortcomings in each major step of [the U.N.] assessment process.”

Though Smith did quote the council correctly, he took those words out of context. Here is the full quote from the InterAcademy Council’s report, in a chapter titled “Evaluation of IPCC’s assessment process:”

InterAcademy Council, 2010: This chapter identifies and recommends ways to address the most significant shortcomings in each major step of IPCC’s assessment process, based on the Committee’s analysis of current IPCC practices, of the literature on assessments, and community input.

The drastically negative tone of Smith’s version is not present in the actual document. Here is how that report’s executive summary characterized its primary findings: “The Committee found that the IPCC assessment process has been successful overall.”

To be clear, the report did find problems with IPCC’s methods and structure, and added that changing circumstances underlying both climate science and the political atmosphere surrounding this issue are important. “The IPCC must continue to adapt to these changing conditions in order to continue serving society well in the future,” the report’s authors wrote.

Though the council clearly believes there are issues to be fixed with IPCC, Smith’s version suggests an unequivocal condemnation — a twisting of a more nuanced message.

Editor’s Note: SciCheck is made possible by a grant from the Stanton Foundation.